1. Field of the Invention
The invention relates generally to rotatable disc cuvette arrays adapted for use in a centrifugal analyzer having means to rotate the array so as to permit measurements of the optical density or absorbence values of light passing successively through each of a series of radially spaced cuvettes during their rotation. In particular, the invention relates to a reusable cuvette array which may be used for chemical analysis, disassembled, easily cleaned and used again.
2. Description of Related Art
Analyzing systems using rotating cuvette arrays are in wide use, particularly for absorbence measurements in connection with analytical apparatus.
Generally, earlier arrays have consisted of an array composed of a number of wedge-shaped, radially disposed cuvettes which extend out from a central hub and which contain, extending radially outwardly from the hub, the following elements: a first annular series of compartments for holding a first substance; an annular series of dividing walls or ramps, one for each cuvette; a second annular series of compartments for holding a second substance which is frequently an unknown sample of blood or other body fluid; and an annular series of vertical end walls. To conduct analysis, the array is rotated at a speed designed to cause the contents of the first chamber of each cuvette to climb over the ramp under centrifugal force and mix and react with the material contained in the second chamber.
A cover is usualy placed over the cuvettes to reduce evaporation and contamination and still provide optical paths so that the contents of the second chamber after reaction may be analyzed through photometric means.
One example of an improvement to this general prior configuration is found in U.S. Pat. No. 4,123,173 issued to Bullock, et al on Oct. 31, 1978. The Bullock array is a less expensive cuvette array compared to those that preceeded it. In selecting materials to help achieve this lower cost, the Bullock device was designed to be disposable, i.e., each cuvette is to be used only once. The Bullock array consists of a number of wedge-shaped cuvettes which are formed by sheet molding. The cuvettes are separate from one another and are divided into an inner and outer pair of compartments. The compartments are divided by a ramp-shaped wall which is inclined on its inner surface while essentially vertical on its outer surface. The outer end of the outer compartment is configured so that fluids flowing outwardly under centrifugal force are forced in toward the radial center by reverse curved side and end walls. This is designed to promote intimate mixing. Further outside the end walls of the cuvettes is a horizontal annular flange.
Circumferentially bonded to this flange is a flexible horizontal annulus formed of thin plastic material having light transmissive properties. The annulus overlies the cuvette end walls and is provided with slots on both its inner edge and outer edge. The slots on the outer edge are provided as an encoding system and are used to provide a zero referencing of the reading of each cuvette during analysis. Bullock, et al provides that the outer portion of the annulus with these encoding slots be made opaque by painting or some other means. The inner edge of the annulus extends to a point just inside the inner ramp wall. The slots provided along this inner edge extend just far enough outward to provide access to the outer compartment.
Both the upper horizontal annulus and the lower cuvette array piece are formed of a thin, flexible thermoplastic material which is generally transparent and which has a high degree of flexibility.
There are several drawbacks however to the configuration used in Bullock, et al. First, the thin plastic material forming the bottom cuvette array portion is so thin that there frequently are breaks and cracks in the outer compartments at the points where severe bending of the plastic occurs during forming. For example, the end walls form a right angle with the lower surface of the outer compartment. At these points the plastic is so thin that cracking and dimpling is a frequent problem. Small leaks in a device which makes measurements based on microliters can create gross inaccuracies in the results. Therefore, improvements with respect to the material and the formation of the cuvettes themselves would be important. Second, the upper horizontal annulus leaves open a considerable amount of the inner compartment of each cuvette. This permits for evaporation and cross-contamination frequently because of splashing. In addition, when either substance is pipetted into one of the compartments, the liquid enters with such force that it frequently splashes; and, unless adequate covering is provided, the splashing will either cause contamination to adjoining cuvettes, or will at least adversely alter the proper proportioning needed for accurate test results. Finally, it would be advantageous to have a disc which is as inexpensive as the Bullock, et al device but would nonetheless be reusable and could be cleaned easily and conveniently after use.
Another multi-cuvette array is shown in U.S. Pat. No. 4,226,531 issued to Tiffany, et al on Oct. 7, 1980. Tiffany, et al shows, like Bullock, et al, a lower cuvette segment and an upper annulus. These two elements are welded together to form a single disposable plastic array. Once again, the array is designed to be thrown away after one use and cannot conveniently be cleaned.
The design in Tiffany is constructed by injection molding and subsequent welding of the lower cuvette array to the upper planar member. Being welded together, the two elements are not readily cleanable. In addition, the square corners and right angle edges shown in Tiffany do not aid mixing as effectively as would rounded edges and corners.
Two patents which incorporate the general structure of Tiffany are U.S. Pat. Nos. 4,314,970 issued Feb. 9, 1982 to Stein, et al and 4,373,812 issued Feb. 15, 1983 to Stein, et al. The Stein '812 patent incorporates Tiffany almost exactly except that capillary flow inhibiting structure has been added t the inner lower edges of each cuvette to help prevent capillary flow during rotation and analysis. The Stein, et al '970 patent, while using the basic Tiffany structure, is considerably more complex in that a number of upper rings are incorporated to help provide specific viewing characteristics.
Finally, U.S. Pat. No. 4,387,992 issued on June 14, 1983 to Swartz shows a cuvette array which is composed of an upper planar member and a number of boat members. These boats are individually attached to the upper planar disc by welding. Because they are permanently attached and because they would have to be cleaned individually, the Swartz array is designed to be disposable. Cleaning of the individual boats would be inefficient. Swartz also makes specific reference to the thickness ratios of the planar member and individual boat walls.